Controversial idea to save corals would replace them with new species

Could drastic action help restore coral reefs?

Serge Melesan / Alamy

Corals are being hit so hard by global warming that the only way to save reef ecosystems may be to replace native species with more heat-tolerant ones from elsewhere in the world. That is the view of two coral researchers who are calling for the benefits and risks of deliberately introducing alien corals to be thoroughly assessed, rather than dismissed out of hand.

Living corals are vital for the health of reefs and the people who depend on them, says Michael Webster at New York University. “Coral does a lot more than just look pretty on the reef. It provides spaces for different organisms to live. It blocks waves from shorelines, it makes the sand for tropical beaches.”

But corals can’t cope with temperatures outside the usual range in their location. As sea temperatures soar due to global warming, widespread bleaching is occurring. This is when corals expel the algal symbionts that provide many of their nutrients, which can ultimately lead to die-off.

“Lots of places around the world are quickly losing their coral, and they are having mixed results in trying to bring it back with more conventional tools,” says Webster.

In an opinion piece written with Daniel Schindler at the University of Seattle, Washington, Webster is calling for change. “You might be able to find corals in a very different place that have already adjusted to the conditions that are arriving at a place, or that might be at that place in the future. You can essentially try and find corals that are pre-adapted,” he says. Many of those trying to save coral reefs are appalled by this idea, but the situation is getting so bad that we need to seriously consider it, says Webster.

For instance, the two species of branching corals native to the Caribbean are in very bad shape, he says. But there are more than 100 species of branching corals globally, some of which could recreate the habitat provided by branching corals if introduced to the Caribbean. “They’re not going to necessarily be the same color or anything like that,” says Webster. “But they’re similar, ecologically.”

Webster and Schindler admit that there are dangers. The worst-case scenario is that devastating diseases or predators are accidentally introduced along with the exotic corals. Introduced corals could also outcompete native species or hybridise with them.

But there is also a risk of waiting too long before doing something, says Webster. He thinks replacing lost species with ones that perform a similar role, which is known as ecological replacement, is much more practical than some other options being explored, such as trying to genetically engineer corals to tolerate greater heat. “Our best bet for coral reefs is the existing diversity that’s out there,” he says.

Terry Hughes at James Cook University in Queensland, Australia, disagrees. “The benign term ‘ecological replacement’ is naïve, dangerous and astonishingly arrogant,” he says. “The authors fail to acknowledge that huge ecological damage has already been inflicted on the world’s coral reefs by accidental and deliberate introductions of exotic species.”

For instance, in the 1980s, an unknown Pacific disease spread out from the Panama canal entrance, wiping out out algae-eating urchins in the Caribbean, leading to rampant algal growth that killed millions of corals, says Hughes. “Invasive species are a problem for coral reefs, and not a sane solution.”

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